Technetium 99m is widely used in the field of nuclear medicine to visualize internal organs with appropriate scintillation scanning equipment. Its short physical half-life (six hours) and low energy gamma ray (140 kev) make it particularly suitable for such use as the radiation dose to the patient undergoing the diagnostic procedure is minimized. Furthermore, generators are commercially available from which this isotope can be eluted from its parent, 2.7 day molybdenum 99, enabling use of the isotope at great distances from the production site. However, its short physical half-life precludes lengthy or involved preparatory procedures and makes it imperative that they be efficient and brief.
.sup.99M Tc in the chemical form of pertechnetate (TcO.sub.4 .sup.-) ion has been used to image some areas of the body, but the biological distribution of the isotope in this form is of an imperfect nature. However, when the technetium is reduced to lower oxidation states it can be efficiently bonded to colloidal material and is then useful for studies of, for example, lung or liver function.
A variety of carries for this isotope have been developed for use in visualizing different organs. For instance .sup.99m Tc-sulfur colloid preparations are known for use in obtaining liver scans but are not ideal in that they involve a protracted period of mixing, heating, and cooling and the particles are not very uniform as to shape or size. Uniformity of shape and size is important for control of radioisotope content, localization in the body and time of elimination from the body. U.S. Pat. No. 3,683,066 is directed to a kit for use in preparing .sup.99m Tc-sulfur colloid.
.sup.99M Tc labelled macroaggregated albumin is widely used for lung scans but might be improved upon as allergenic reactions may occur. U.S. Pat. Nos. 3,663,686 and 3,663,687 are directed to the use of spherical particles of parenterally metabolizable protein as the carrier for radioisotopes such as .sup.99m Tc. They relate particularly to the preparation of the spherical particles to control the size range, the radioactive labelling process being carried out either before or after particle formation. The control of particle size range is for the purpose of controlling localization within the body. The particle size range is determined, however, during formation of the spherical particles by controlling parameters relating to dispersion of the protein in a suitable liquid. Proteins such as albumin, gelatin, hemoglobin and the like are indicated.
U.S. Pat. Nos. 3,663,687 and 3,725,295 disclose reduction of the .sup.99m pertechnetate ion to a lower oxidation state for combination with carrier, using for example ascorbic acid and ferric ion, or stannous ion as the reducing agent.
A recently published article, "Distribution and Fate of Synthetic Lipid Vesicles in the Mouse: A Combined Radionuclide and Spin Label Study," I. R. McDougall et al, Proc. Nat. Acad. Sci. USA 71, No. 9 pp 3487-3491, Sept. 1974, describes the distribution in the mouse of lipid material using .sup.99m Tc as tracer. The tracer is in the form of pertechnetate anion and is encapsulated within lipid membrane enclosed compartments. These vesicles can be easily disrupted, however, in the body and then the tracer is transported independently of the carrier.